Use platform drags for drags of docks and toolbars on wayland

On Wayland we can't know where windows are in relation to
each other so the whole mechanism was broken, toolbars
were unmovable once undocked and could be blindly redocked.
Dockwidgets had native toolbars to move them around but could
not be redocked.
This introduces an alternative code path that uses a platform
drag with a special mimetype that enables the platform to
issue a combined drag and window move using the relevant protocol.
Should the protocol not be available this doesn't make things
actively worse as it will be similar broken as before.

Fixes: QTBUG-87332
Change-Id: I3b8bdc0b1bc22569a64cb8bf7ca7d37d223936a6
Reviewed-by: David Edmundson <davidedmundson@kde.org>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/src/widgets/widgets/qmainwindow.cpp b/src/widgets/widgets/qmainwindow.cpp
index a5f7973994..0fc8aeace7 100644
--- a/src/widgets/widgets/qmainwindow.cpp
+++ b/src/widgets/widgets/qmainwindow.cpp
@@ -25,6 +25,7 @@
 #include <qstyle.h>
 #include <qdebug.h>
 #include <qpainter.h>
+#include <qmimedata.h>
 
 #include <private/qwidget_p.h>
 #if QT_CONFIG(toolbar)
@@ -36,6 +37,8 @@
 
 QT_BEGIN_NAMESPACE
 
+using namespace Qt::StringLiterals;
+
 class QMainWindowPrivate : public QWidgetPrivate
 {
     Q_DECLARE_PUBLIC(QMainWindow)
@@ -121,6 +124,7 @@ void QMainWindowPrivate::init()
     const int metric = q->style()->pixelMetric(QStyle::PM_ToolBarIconSize, nullptr, q);
     iconSize = QSize(metric, metric);
     q->setAttribute(Qt::WA_Hover);
+    q->setAcceptDrops(true);
 }
 
 /*
@@ -1296,6 +1300,22 @@ bool QMainWindow::event(QEvent *event)
             if (!d->explicitIconSize)
                 setIconSize(QSize());
             break;
+#if QT_CONFIG(draganddrop)
+        case QEvent::DragEnter:
+        case QEvent::Drop:
+            if (!d->layout->draggingWidget)
+                break;
+            event->accept();
+            return true;
+        case QEvent::DragMove: {
+            if (!d->layout->draggingWidget)
+                break;
+            auto dragMoveEvent = static_cast<QDragMoveEvent *>(event);
+            d->layout->hover(d->layout->draggingWidget, dragMoveEvent->position().toPoint());
+            event->accept();
+            return true;
+        }
+#endif
         default:
             break;
     }